The present invention relates to a fixing device for allowing a recording medium on which a toner image is electrostatically transferred to pass therethrough, heating the toner image and pressurizing the recording medium such that the toner image is permeated on the recording medium, and fixing the toner image on the recording medium.
A device using an endless fixing belt is known as a conventional device built in a printer or a copier. In the device of this type, an endless fixing belt is put round a plurality of rollers and stretched, a pressurizing roller is arranged to pressurize the surface of the fixing belt, the fixing belt is heated, a recording medium on which a toner image is transferred is conveyed between the fixing belt and the pressurizing roller, and the toner image is heated, pressurized and thereby fixed on the surface of the recording medium.
A device disclosed in, for example, Jpn. Pat. Appln. KOKAI Publication No. 2000-66541, is known as a fixing device using a fixing belt. This fixing device is provided on a printer body so as to be detachable therefrom. This device is assembled by providing a unit in which an endless fixing belt is put round a heater-incorporated heating roller and a fixing roller, and the heating roller and the fixing roller are integrally mounted in a cover, to a device body containing a pressurizing roller so as to be detachable therefrom. The fixing belt is heated by the heater incorporated in the heating roller. A sheet on which a toner image is transferred is conveyed between the pressurizing roller and the fixing roller round which the fixing belt is put, and the toner image is fused and fixed on the sheet by heat supplied from the fixing belt. The unit can be easily exchanged and maintenance can be facilitated by mounting a unit in which members such as the fixing belt having a comparatively short life are integrally provided in the fixing device body so as to be detachable therefrom.
A device disclosed in Jpn. Pat. Appln. KOKAI Publication No. 8-292669 is also known as another fixing device using a fixing belt. In this fixing device, an endless fixing belt is put round three rollers including a drive roller and stretched, a heater is arranged inside the fixing belt, and a pressurizing roller is arranged to pressurize the drive roller by the fixing belt. The fixing belt is heated from a back side thereof by the heater. A sheet on which a toner image is transferred is conveyed between the pressurizing roller and the drive roller round which the fixing belt is put, and the toner image is fused and fixed on the sheet by heat supplied from the fixing belt.
In the device disclosed in Jpn. Pat. Appln. KOKAI Publication No. 2000-66541, since the fixing belt is heated by the heater incorporated in the heating roller, heat from the heater transmits to the heating roller, the back surface of the fixing belt and the top surface of the fixing belt in order, much time is required to raise the temperature of the surface of the fixing belt to a desired temperature, and much time is also required to warm up the fixing device. Further, for example, since heat escapes to the cover through the rotary shaft of the heating roller, more thermal energy than necessary is required to raise the temperature of the surface of the fixing belt to a desired temperature and power consumption is thereby increased.
In the device disclosed in Jpn. Pat. Appln. KOKAI Publication No. 8-292669, the belt is directly heated by the heater arranged inside the fixing belt. However, since the heat from the heater transmits to the back surface of the fixing belt and then to the top surface of the fixing belt, for example, heat escapes through rotary shafts of three rollers that are in contact with the back surface of the fixing belt, and much time and much energy are required to raise the temperature of the surface of the fixing belt to a desired temperature.
The present invention is accomplished in consideration of the above points, and an object of the present invention is to provide a fixing device capable of reducing power consumption and shortening a warm-up time.
Another object of the present invention is to provide a fixing device which allows the only fixing belt having a comparatively short life to easily exchange and which can thereby reduce maintenance costs.
To achieve the above objects, there is provided a fixing device for allowing a sheet-like recording medium on which a developer image is transferred to pass through a conveyance path and fixing the developer image on the recording medium, the fixing device comprising:
a first roller and a second roller arranged opposite to one another to sandwich and mutually pressurize the conveyance path, the first roller arranged on the surface side of the recording medium conveyed in the conveyance path;
an endless belt put round a part of the first roller, for running while an outer surface thereof is in contact with the surface of the recording medium conveyed in the conveyance path, the belt being longer than an outer periphery of the first roller; and
a heater for heating the belt.
Further, there is provided a fixing device for allowing a sheet-like recording medium on which a developer image is transferred to pass through a conveyance path and fixing the developer image on the recording medium, the fixing device comprising:
a first roller and a second roller arranged opposite to one another to sandwich and mutually pressurize the conveyance path, the first roller arranged on the surface side of the recording medium conveyed in the conveyance path;
an endless belt put round the first roller and stretched, for running while an outer surface thereof is in contact with the surface of the recording medium conveyed in the conveyance path;
a third roller having an outer peripheral surface that is in contact with an inner surface of the belt, and being urged in a direction of separating from the first roller so as to apply tension to the belt, the third roller having a smaller diameter portion that is made narrow to reduce an area of the outer peripheral surface; and
a heater for heating the belt.
Moreover, there is provided an image forming apparatus comprising:
image forming means for forming an image of a developer on an image carrier;
a transfer device for transferring the developer image formed by the image forming means on a surface of a sheet-like recording medium;
a conveyance path in which the recording medium on which the developer image is transferred by the transfer device is conveyed; and
a fixing device for fixing the developer image on the recording medium conveyed in the conveyance path,
the fixing device comprising:
a first roller and a second roller arranged opposite to one another to sandwich and mutually pressurize the conveyance path, the first roller arranged on the surface side of the recording medium conveyed in the conveyance path;
an endless belt put round a part of the first roller, for running while an outer surface thereof is in contact with the surface of the recording medium conveyed in the conveyance path, the belt being longer than an outer periphery of the first roller; and
a heater for heating the belt.